Any member of the deer family, such as moose, elk or deer. Often an expression of surprise upon spotting a deer or moose in an unexpected environment. Mook may be a contraction of, "Moose! Look!" Mook is of uncertain origin, but may have its roots in baby talk. Mook is an expression used more commonly by city dwellers than country folk.

Look at that mook eating up the neighbor's prize fruit trees!

At the cabin: "What's that animal in the field?" "I dunno. Some kind of mook!"